Cathode ray tube, and particularly color cathode ray tube manufacturing requires fabrication of a viewing screen structure, having a number of phosphor fields and usually a matrix of opaque material surrounding the phosphors and affixed to the inner surface. As is well known, the phosphor and matrix configuration are both intricate and precise requiring extensive controls, special apparatus, and knowledge in order to provide an acceptable commercial product.
At present, the most common practice for designing lens structures for color cathode ray tubes of the so-called "shadow mask" type includes the selection of a number of "shadow mask" coordinates. A light source is directed through a flat glass surface toward the "shadow mask" to print a phosphor field on the panel or viewing screen.
The viewing screen with the affixed phosphors has a plurality of data points and is fabricated into a color cathode ray tube. A measurement is made of the mislanding or deviation of electron beam landing from the phosphors at the data points. Then, a lens surface is calculated to provide proper beam landing at the data point coordinates.
A lens is constructed from the information provided and utilized, with a light source, to construct a viewing panel having phosphor locations as determined by the lens system. The viewing panel is fabricated into a cathode ray tube and a measurement of mislanding or deviation of electron beam landing from the data points is again made. This information is employed to calculate a new lens surface for effecting a proper beam landing and another new lens fabricated for use in manufacturing a color cathode ray tube. Moreover, the process is repeated until a lens is suitable to the fabrication of acceptable viewing screens for cathode ray tubes is produced.
Although the above-described cathode ray tube lens fabricating process has and still does provide readily marketable color cathode ray tubes and lenses for fabricating the color cathode ray tubes, it has been found that the process leaves something to be desired. More specifically, it has been found that the above-described lens fabricating process is relatively slow in that each iterative design requires a new lens fabrication at a considerable cost in time, labor, and materials.